"The Response of Radiative Feedbacks and Equatorial Pacific Seasonality to Orbital Forcing"

Abstract:
Past changes in the Earth’s orbital properties led to dramatic changes in the Earth’s climate. To investigate the effects of this orbital forcing on the climate system, idealized simulations are conducted with the GFDL CM2.1, an atmosphere-ocean general circulation model, in which obliquity, eccentricity, and longitude of the perihelion are altered while other forcings, such as ice sheets and atmospheric composition, are held at preindustrial levels. Because only the Earth’s orbit is changed in these simulations, the climate response to obliquity and precession may be isolated, and two aspects of the response are explored in particular: radiative feedbacks and changes in equatorial Pacific seasonality. While changes in obliquity and longitude of the perihelion simply redistribute insolation without altering its global, annual-mean value, radiative feedbacks – changes in surface albedo, water vapor, lapse rate, and clouds – can lead to significant global-mean temperature response: -0.5 K in a lowered obliquity experiment and +0.6 K in an altered longitude of perihelion experiment. Additionally, in the Arctic, cloud feedbacks damp the reduction of summer insolation at times when orbital forcing should promote glaciation, perhaps presenting an additional hurdle for glaciation. In the equatorial Pacific, the seasonal temperature cycle responds strongly to precession. Part of this seasonality change is a direct thermodynamic response to changing insolation, but some of the change may be attributed to changes in strength of the subtropical anticyclones and changes in convection over the western equatorial Pacific. Such changes in equatorial Pacific seasonality could be misinterpreted as ENSO variations in proxy records which lack sufficient time resolution.

"Convective Dynamics in the Interiors of Ice Giants and Icy Satellites"

Abstract:

Rotating convection is ubiquitous across the solar system and responsible for a wide range of phenomena, including planetary magnetic fields, atmospheric winds, and ocean currents. Here I will focus on the internal dynamics of ice giants and icy satellites.

The ice giant planets, Uranus and Neptune, have magnetic fields, atmospheric circulation patterns, and thermal emissions that are distinct from other planets in our solar system. However, no self-consistent model has been able to reproduce all of these observations. We hypothesize that the magnetic fields and surface winds are dynamically coupled and argue that their characteristics are a consequence of quasi-three-dimensional convective turbulence. I will present dynamo models that, in agreement with observations, generate multipolar magnetic fields, produce three east-west jets, and predict local equatorial peaks in internal heat fluxes. Thus, we argue that convection weakly constrained by rotation can explain the first-order geophysical observations of the ice giants.

The icy Jovian satellite Europa maintains a global liquid water ocean between a lower silicate mantle and an upper ice shell. We use state-of-the-art rotating convection theory to predict that Europa's ocean is characterized by quasi-three-dimensional convective turbulence, similar to the interiors of Uranus and Neptune. I will present a global ocean convection model and show that large-scale currents are organized into three east-west jets and two equatorial Hadley-like circulation cells. These motions transmit the satellite's internal heat most effectively in the equatorial region, which can directly influence the latitudinal thermo-compositional state and structure of the ice shell. This heterogeneity may promote the formation of chaos features, regions of disrupted ice that occur more prevalently at low latitudes, through increased melting of the ice shell near the equator and subsequent deposition of marine ice.

2014 IX Latin American Forum on Energy and the Environment

The 2014 IX Latin American Forum is a unique by-invitation-only event that addresses a critical need to bring together government and industry decision makers, scholars and scientists, to foster dialogue around geosciences, technology, and energy and environmental policy issues. The University of Texas at Austin’s Jackson School of Geosciences hosted the IX Latin American Forum on Energy and the Environment with collaboration from the Ministry of Energy and Energy Affairs of the Republic of Trinidad and Tobago on Monday March 24, 2014. This year’s theme was Natural Gas-LNG: An Atlantic Basin Perceptive and the role it plays in the Caribbean and Latin America.

In 2010-2011, the city of Christchurch, New Zealand was devastated by a series of powerful earthquakes, the most destructive being the 22 February 2011 Mw6.2 Christchurch Earthquake. This event resulted in 185 casualties, thousands of injuries, and widespread soil liquefaction that caused billions of dollars in damage to buildings, homes and infrastructure. Ultimately, as a result, approximately 7,500 homes have been abandoned and an estimated 80% of the structures within the Christchurch central business district have been demolished.

A network of 19 seismic recording stations in the greater Christchurch area captured an extensive and unique set of ground motions (GM) during the 2010-2011 earthquakes. Potentially, these GM can be used for back-analyses aimed at understanding the spatial variability of the ground shaking (particularly site and basin effects) during each event, followed by accurate forward-estimates aimed at quantifying the amplitude and frequency content of future design GM. However, detailed GM analyses cannot presently be conducted because little information exists on the shear wave velocity (Vs) structure of the greater-than-400-m deep interlayered alluvial sand and gravel deposits that underlie Christchurch.

My research team recently conducted deep Vs profiling at 15 strategic locations throughout Christchurch with the goal of developing a seismic velocity model for the Canterbury basin. The deep Vs profiling was performed using a combination of large active-source and ambient-wavefield surface wave testing. The dispersion estimates from the active-source and ambient-wavefield data at each site were combined to produce an inter-method composite dispersion curve with associated data uncertainty bounds. After which, the open-source software package Geopsy was used to perform a multi-mode, joint inversion of the dispersion data, the SPAC curves and the peak frequency of the mean horizontal-to-vertical (H/V) spectral ratio curve for the site. Rather than providing a single, deterministic Vs profile for each site, these inversions have been used to provide a suite of profiles that fit the experimental data equally well, given the estimated data uncertainty. While results are still preliminary, this work has resulted in Vs profiles that extend a minimum of several hundred meters and a maximum of greater than 1km below the ground surface. This research has more than tripled the available comparisons between large active-source and ambient-wavefield surface wave methods utilized for deep Vs profiling. These comparisons are needed before confidence in utilizing passive-wavefield methods independently can be achieved.